1. Field of the Invention
The present invention relates to a pattern forming method and a charged particle beam writing apparatus.
For example, the present invention relates to a dimension correction method in electronic beam writing which writes a pattern by using an electron beam.
2. Related Art
A lithography technique which makes the advance of miniaturization of a semiconductor device is a very important and an only process which generates a pattern in semiconductor manufacturing processes. In recent years, with a high degree of integration of an LSI, a circuit line width required for a semiconductor device is miniaturized every year. In order to form a desired circuit pattern to the semiconductor device, a high-precision master pattern plate (also called a reticle or a mask) is necessary. An electron beam writing technique inherently has an excellent resolution and is used in production of a high-precision master plate or a mask.
FIG. 11 is a conceptual diagram for explaining an operation of a conventional variable shaping electron beam writing apparatus.
In the variable shaping electron beam (EB) writing apparatus, a pattern will be written as follows. In first aperture 410, an oblong (for example, rectangular) opening 411 to shape an electron beam 330 is formed. In a second aperture 420, a variable shaping opening 421 to shape the electron beam 330 passing through the rectangular opening 411 into a desired oblong shape is formed. The electron beam 330 irradiated from a charged particle source 430 and passing through the rectangular opening 411 is deflected by a deflector. The electron beam 330 passes through a part of the variable shaping opening 421 and is irradiated on a target workpiece 340 placed on a stage. At this time, the stage continuously moves in a predetermined direction (for example, an X direction). More specifically, an oblong shape which can pass through both the rectangular opening 411 and the variable shaping opening 421 is written in a writing region of the target workpiece 340. A scheme which causes an electron beam to pass through both the rectangular opening 411 and the variable shaping opening 421 to form an arbitrary shape is called a variable shaping scheme. With respect to the variable shaping electron beam writing apparatus, disclosed documents are present (for example, see Published Unexamined Japanese Patent Application Publication No. 9-293670 (JP-A-9-293670)).
A resist film is coated to the target workpiece 340. The electron beam 330 is irradiated on the resist film to form a pattern. The pattern is developed to form a resist pattern. By using the resist pattern as a mask, an underlying light-shielding film is etched. The resist pattern is removed, and cleaning is performed, so that a mask for exposing a semiconductor device pattern, for example, is completed.
In this case, as a material of the resist film for an electron beam, a chemical amplification type resist is used. However, the chemical amplification type resist has a problem that resist sensitivity irregularity occurs between mask substrates and in a substrate. For this reason, a variation in pattern dimension CD is caused. Therefore, the precision of the CD is consequently deteriorated. In particular, the precision of the CD deteriorates in a so-called global region whose influence range is the order of a few millimeters to a few centimeters. In a conventional technique, a variation in global CD suddenly occurs, and the variation cannot be detected until a pattern is developed. For this reason, the variation is difficult to be corrected in advance. Not only the resist sensitivity irregularity, but also development irregularity or resist coating irregularity causes a variation in CD. Consequently, the precision of the CD is deteriorated.
As described above, the resist sensitivity irregularity, the development irregularity, or the resist coating irregularity causes a variation in CD and deteriorates the precision of the CD. For this reason, it is desirable to correct the variation in CD and the precision of the CD in pattern writing. Effective means to solve the problems is not conventionally established.